With rapid development of the communications market, a module between digital and analog in an integrated circuit becomes increasingly important. In applications in the video and wireless fields, a digital-to-analog converter (DAC) needs to have a high speed and high precision. A current steering DAC is widely applied to integrated circuits, and a current steering structure has advantages of a high speed, high precision, and ease of complementary metal-oxide-semiconductor (CMOS) current integration.
FIG. 1 is a structural diagram of a DAC having a three-state structure provided in the prior art. The structure of the DAC mainly includes two parts: N current modules (ICELL1, ICELL2, . . . , ICELLN) and a current-to-voltage conversion module. The current module is configured to convert a digital signal into an analog current. Each current module includes one logical conversion unit and one current unit. The logical conversion unit is configured to convert an input digital signal DIN into a switch control signal that is used to control the current unit to operate normally or stop operating. The current unit controls, based on the received switch control signal, a signal switch included in the current unit to be opened or closed, so as to operate normally or stop operating. Each current module outputs two differential current signals to the current-to-voltage conversion module. The current-to-voltage conversion module is configured to convert an analog current signal that is output by the current module into an analog voltage signal.
The current module ICELL1 is used as an example in FIG. 1. The ICELL1 includes two current sources Ip and In that are used to provide a current respectively to an upper MOS transistor and a lower MOS transistor. AVADD represents a source voltage. AGND represents grounding. A bias voltage VBP is used to provide a voltage to a gate of the upper MOS transistor, and a bias voltage VBN is used to provide a voltage to a gate of the lower MOS transistor. In addition, the current module includes three parallel switch branch circuits. One switch branch circuit includes two SZ signal switches connected in series, and the other two switch branch circuits each include an SN signal switch and an SP signal switch connected in series. A drain of the upper MOS transistor and a drain of the lower MOS transistor are separately connected to the three parallel switch branch circuits, and separately obtain two differential current signals from the foregoing two branch circuits constituted by the SN signal switch and the SP signal switch connected in series and provide the two differential current signals to an operational amplifier (OPA) of the current-to-voltage conversion module. In addition to the OPA, the current-to-voltage conversion module further includes two resistors R1 and R2. The R1 is connected between a positive input end and a negative output end of the OPA, and the R2 is connected between a negative input end and a positive output end of the OPA. The current-to-voltage conversion module outputs two analog voltage signals OUTP and OUTN by using the OPA.
For a design of the DAC having such a structure, to reduce a jitter of a current unit in the DAC and reduce nonlinearity of the DAC, not all switches of all current units in the DAC are opened at the same time, that is, not all of the current units are in a non-operating state. Therefore, regardless of a value of a signal amplitude, each current unit in the DAC has a current, leading to power consumption. Consequently, power consumption of the entire DAC is relatively high.